Control system for furnaces



Nov. 30, 1943.

c. H. DlCKE CONTROL SYSTEM FOR FURNACES Filed Jan. 21, 1941 I. SEASON 5 /A/0mz OPEN 44 B/ISE MEN 7" J6 SWITKH LIMIT SWITCH iNVENTOR ATTORNEYS Patented Nov. 30, 1943 CONTROL SYSTEM FOR FURNACES Carl H. Dicke, Dayton, Ohio, assignor to The Master Electric Company, a corporation of Ohio Application January 21, 1941, Serial No. 375,143

5 Claims.

This invention relates to improvements in control system for furnaces, and more particularly for furnaces adapted to alternatively burn two types of fuel.

An object of this invention is to provide an arrangement for improving the year-round operation of furnaces.

Another object of this invention is to provide an improved controlling system for furnaces adapted to burn two types of fuel, such as coal and gas.

Still another object of this invention is to provide an economical, efficient, automatic and reliable control system for furnaces adapted to burn solid and gaseous fuel.

A further object of this invention is to control a furnace burning both solid or gaseous fuel in accordance with the will of the operator, by a single automatic temperature-responsive unit.

A still further object of this invention is the provision of an arrangement whereby a furnace may be changed over from solid to gaseous fuel operation, and vice versa, in the simplest possible manner.

A more specific object of this invention is to provide a correlated solid and gaseous fuel burning control system for furnaces, wherein the change-over from solid to gaseous fue1 and vice versa is accomplished in the simplest possible manner from a single temperature-responsive unit, and the optimum conditions for either fuel burning operation are automatically assured.

These and other features, capabilities and advantages of the invention will appear from the subioined detailed description of one embodiment and a modification thereof, illustrated in the accompanying drawing, in which:

The single figure is a circuit diagram of a preferred control system in accordance with the present invention, wherein the furnace damper and a gas valve are controlled by a single room thermostat.

One form of the invention as illustrated in the drawing, illustrates a control system for a furnace generally indicated at 2 adapted to be supplied with both solid and fluid fuel. The furnace 2 will have suitable fire-controlling dampers for use in connection with the solid fuel, such as the draft damper 4, and means such as the pipe 6 for the entrance of the fluid fuel, which may be, for example, gas. The furnace is primarily under the control of ;a suitable temperature-responsive device such as the usual room thermostat 8, adapted to open at a predetermined temperature and to close at a lower predetermined temperature, as is well known in the art. The latter is adapted to control the opening and closing of the dampers by suitable means such as the damper motor generally indicated at I0, and the magnetically operated, normally closed gas valve l2, depending upon the position of the season switch 14, in a manner to be described in more detail hereinafter. The system may also include a suitable basement switch I6 for use in connection with the firing of the solid fuel.

The control system preferably, but not necessarily, is a low-voltage system taking its power from the usual supply means [8 through a suitable transformer 26.

As shown in the drawing, the furnace damper is closed, the season switch is in position for use with solid fuel, the basement switch is in its normal position and the room thermostat does not call for heat.

Assuming now that the temperature of the space to be heated is sufiiciently low so that the room thermostat will close its contacts, such closing will complete a circuit which may be traced from one end of the transformer secondary winding 22, conductors Hand 26, contact arm 28 and contact 30 of the season switch I4, conductor 32, contact arm 36 and contact 38 of the basement switch l6, conductors 40 and 42, closed contacts 44 and 4B and arm 48 of the room thermostat 8, conductors 50 and 52, a suitable limit switch 54 of any well-known type, conductor 56, contact arm 58 and contact 60 of season switch l4, conductor 62, winding 64 of-control relay 66, and conductors 68, 10, 12 and 14 to the other side of the transformer winding 22. The winding 64 being connected to the transformer secondary through the circuit just traced will move the relay 66 to establish a circuit for the damper motor to open the draft damper 4. This circuit may be traced from one end of the transformer secondary Winding 22, conductors 24 and 16, motor winding 18, conductors and 82, armature84, bridging contacts 86 and 88 of the relay 66, conductor 90, brush 92, commutator segment 94,

brush 9% and conductors 98, 12 and 14 to the other side of the winding 22. The damper motor 18 accordingly now starts to rotate, and as it rotates the commutator 94 will also rotate in a direction so that brush 92 will meet the cut-out section loll, thus breaking the motor circuit through that brush. However, before th commutator has moved this far, the brush 192 will leave the cut-out section Hi4 and engage the commutator 24, thus maintaining the motor circuit through conductor I26, brush I02, commutator 94, to brush 96 independently of the brush 92 and of the circuit established through the relay 66. The motor will continue to rotate until the commutator has moved approximately 180", or until the brush IE2 is now in the cut-out section I66, at which time the energizing circuit for the motor I8 will be entirely interrupted. However, at this point, a suitable crank I III driven by the motor IB and interconnected with the draft damper 4 by suitable means such as a chain II Z will have moved. the damper to the open position, to increase the combustion in the furnace in accordance with the call of the room the'rmost'at.

If new the room thermostat is satisfied as a result of the increased heat, the'contacts 44 and 46 thereof will open, breaking the previously traced circuit for the winding 64 of the control relay 66. The relay will then return to the: positionillu'strated, armature II'E bridging the contacts H6 and 'I I8. Because the damper is'open and the motor has moved 180, the commutator will have "been displaced 180 so that in its new position an energizing circuit for the damper motor "I8 will now be established to close the draft damper. This circuit may be tracedfrom one end of the transformer secondary winding '22, conductors '24 and TB, damper motor 18, conduc'tor 80, contacts H6 and I I8 bridged 'by the armature II4 of the dc-energized relay 66, conductor I20, brush I22 which will now be in contact with the commutator 9'4, brush 9'6,and-conductors '98, I2 and 'Mto the other "side-of winding 22. After the damper motor and commutators have moved slightly in "a direction to close the damper, the brush I22 will fall within the cutout'section 'I'lll) of the commutator, but again just before this happens the brush 1 92 will have contacted the commutator 94, maintaining th ene'rgizing circuit for the motor I8 as previously traced when the meter was raising the draft damper. Also, similarly, when the motor has rotated approximately 180 and the draft damper is now closed, the brush III-2 will fall within the cut-out portion I24, so that the-motor will stop and the damper remains closed.

If desired, a suitable pilot and heat-anticipating lamp I24 may be used :in connection with the room thermostat 8, in a manner well known to the art. This pilot lamp I24 will-only be lighted when the thermostat is closed, through a icircui-t which maybe traced from one end of the transformer secondary winding 22, conductors 24 and 26, contact arm 23 and contact 30 of the season switch I4, conductor 32, contact arm 36 and contact 38 of basement switch I6, conch-rotors 4 8 and 42, closed contacts 44 anddfi and arm 48 of the room thermostat 8, conductor 5e and I23, lamp I24, and conductors I26 and M, to the other side of winding 22.

If at any time as during the spring an earl fall it is desired to operate the furnace on gas, the season switch I l, as seen'ih'the drawing, is thrown to the left so that contact arms 28 and 5B engage contacts I32 and 132 respectively. This removes the damper motor Ii) from con'trol by the room thermostat 8 by breaking th -cir'cuit previously established through contact '60 to the control relay 65. At the same time, the control relay '66 of necessity being in its offf position, if the furnace dampersare open when the season switch is changed, such dampers will be closed by dropping of the relay in the same manner as though the contacts of the room thermostat had opened; such circuit for closing the draft damper was previously traced in connection with operation by the room thermostat. This provision is extremely advantageous in that it is most desirable when using the gas fuel that the draft damper be closed o as not to interfere with the action of the gas burner, while at the same tim the check damper (not shown) should be open. It is, of course, to be understood that in accordance with the usual arrangement that the furnace is probably provided with the usual check damper which will be open when the draft damper is closed, and vice versa.

Assuming that the season switch is now in position for control of the gas, if the space to be heated drops below a predetermined temperature andthe room thermostat calls for heat, a

circuit will be established which may be traced from'one end of the transformer secondary winding 22 conductors 24 and 26, contact arm 28 and contact I 3fl of the season switch M, conductor 42, closed contacts 44 and d5 andarm 5.8 of the thermostat 8, conductors 56 and 52,liinit switch 54, conductor 56, contact arm 58 and contact I32 of season switch I l, conductor a suitable safety thermostat I35, normally closed in response to the heat from gas pilot 43?, conductor I 38, energizing coil I lli of ga valve i2, and conductors I42, 1B, 7 2 and M to the other side of the winding 22. 'Energization of the coil I40 in this manner opens the valve 12 to permit the flow of suitable'gas. The details of such valve, forming no part of the present invention and well known to the. art, have not been illustrated. When the room thermostat is satisfied and the contacts 44 and i8 opened, the coil Iii) will, of course, become tie-energized and'the valve I2 will automatically move to cut off the gas supply.

Attention is directed to the fact that the pilot lam-p I24 will operate upon closure of the room thermostat 8 when used in connection with the control of the gas valve, as well as with the control of the damper. The conductor 50 being energized by the circuits just previously traced upon closure of thermostat contacts as and it, a circuit for the lamp I24 will follow through conductor I28, lamp I24, and conductors E26 and 14 to 'thetr'ans'former secondary winding 22.

The basement switch 15 is usable with the 'aforedescribed system, in the usual manner. If the basementswitch is moved from its normal to its open position, and the season switch is in positio'n to control thesolidfuel, thecontacts Adand 86 of the room thermostat 8 are effectively shunted and the draft damper will be raised for firing purposes. The control circuit established by moving the basement switch to the open position may be traced from one end of the transformer secondary winding 22, conductors 24 and'26 contact arm '23 and contact 36 pi the season switch I4, conductor 32, contact arm '36 and contact lid of basement switch It, conductor I46, limit switch 54, conductor -56, contact arm 58 and contact-8i] of season switch 'I-E,-conductor '62, winding 64 of relay and-conductors 63 ,75), I2 and M to the-other side of winding 2 2. Wind'- ing 64 thus being energized will raise relay "$6, establishing circuit's'f'or the damper motor to raise the draft damper d, in a manner previously described. When the basement switch *lB-is returned to the nor'mal position-,w mding 6 3 will become de-energizedan'd thedainp'er motor 18. will return'the draft damper to the clos'ed 'position, 'th'r'ough circuits previously described,

less, in the meantime, the contacts 44 and 46 of the room thermostat happen to have become closed. It is also to be noted that when the basement switch It is in the open position, the pilot lamp I24 will be lighted, just as though the room thermostat were closed, accordingly indicating that the draft damper is open. The circuit for this lamp may be traced from one end of the transformer secondary winding 22, conductors 24 and 26, contactarm 28 and contact 30 of season switch 14, conductor 32, contact arm 36 and, contact, 144 of basement switch I6, conductors I46, 52 and I28, lamp I24 and conductors I23 and 14 to the other side of winding 22.

Attention is also directed to the fact that movement of the basement switch from its normal to its fopen position is entirely ineffectual to open the draft damper if the season switch is in the gas-controlling position. This fact will be apparent from a study of the illustrated circuits which show that the energizing circuit for -control winding 64 of relay 66 must always pass through the season switch l4 when in the solid fuel controlling position, so that when the season switch is in the gas-controlling position, no circuit for coil 64 can possibly be established, no matter what the position of the basement switch I6.

Various changes in the above-described system will occur to those skilled in this art and are contemplated as forming part of the present invention. For example, additional safety limit switches may be added to the system where deemed desirable. While the system has been illustrated as operated upon low voltage, by a proper choice of equivalent parts the systems may be used on any ordinary voltage. Additionally, the various units forming the system have been diagrammatically indicated by way of illustration, and it will be obvious that well-known equivalent parts can be used in place of those shown.

While, for the sake of simplicity, the damper motor has been illustrated as operating only a draft damper, it is to be understood, that in accordance with usual practices, and as previously pointed out, the damper motor may also operate a correlated check damper.

It has been found that the system described is unusually well adapted to control furnaces burning solid and gaseous fuel, since, in the fall and spring months a desirable level of heat is diflicult to obtain with solid fuel alone, whereas gas is ideally suitable for heating at this time. Accordingly, it is contemplated that during the cold winter months the furnace will be run on solid fuel, while during the fall and spring months the season switch will be thrown so that the furnace will run upon gas. However, it is clear that the invention in its broader aspect is not limited to such operation, but is generally adaptable for the control of a furnace burning solid and fluid fuel at any time. The control thermostat need not necessarily be a room thermostat and, the fuel, so far as the control system is concerned, could be, for example, oil as well as gas.

Accordingly, while I have herein shown and described only certain embodiments of certain features of my invention, it is to be understood that they are to be regarded merely as illustrative and that I do not intend to limit myself thereto except as may be required by the following claims:

1. Controlling system for a furnace adapted to burn both solid and gaseous fuel, said furnace having at least one controlling damper movable between fire-retarding and fire-accelerating positions and a gas supply, the combination of a source of power, a damper motor for moving said damper from one of said positions to the other, a normally closed gas valve for controlling said gas supply, an actuating winding for opening said valve, a room thermostat having a pair of contacts adapted to open at a predetermined temperature and to close at a lower predetermined temperature, a relay having a pair of normally closed contacts and a pair of normally open contacts, an energizing winding for said relay to close said normally open contacts and open said normally closed contacts, a double-pole doublethrow season switch, means connecting said damper motor to said source of power to move said damper to the fire-retarding position in the normally closed position of said relay and connecting said damper motor to said source of power to move said damper to the fire-accelerating position when said relay is energized, means connecting said relay winding to said source of power through the closed contacts of said thermostat in one position of said season switch, and means connecting said valve-actuating winding to said source of power through the closed contacts of said thermostat in the other position of said season switch.

2. The combination according to claim 1, in combination with a single-pole double-throw basement switch serially connected between said thermostat and said source of power in on position, and movable to a second position to energize said relay winding from said source of power irrespective of the position of said thermostat.

3. The combination according to claim 1, in combination with a single-pole double-throw basement switch serially connected between said thermostat and said source of power in one position, and movable to a second position to energize said relay winding from said source of power irrespective of the position of said thermostat, and means for connecting said basement switch in its second position to said relay winding through the season switch in its one position, whereby movement of said season switch to its other position disconnects said winding from the source of power irrespective of the position of said basement switch.

4. Controlling system for a furnace adapted to burn both solid and gaseous fuel, said furnace having at least one controlling damper movable between fire-retarding and fire-accelerating positions, and a gas supply, the combination of a source of power, electrically energizable means for controlling said damper, electrically energizable means for controlling said gas supply, a thermostatically operated switch, a switch device electrically alternatively interconnecting said thermostatically operated switch and said source of power with either one of said electrically energizable means, while simultaneously disconnecting the other electrically energizable means from said source of power and said thermostatically operated switch, and means for interconnecting the electrically energizable damper controlling means to said source of power for moving said damper to the fire-retarding position if in the fire-accelerating position in response to the call of said thermostatically operated switch, whenever said switch device is moved to the position for controlling the electrically energizable gas supply controlling means.

5. Controlling system for a furnace adapted to turn both sol-id and gaseous fuel, said furnace having at least one controlling damper movable between fire-retarding and fire-accelerating positio'ns, and a gas supply, the combination of a source of power, a damper motor for moving said damper from one of said positions to the other, a solenoid-operated gas valve,-a room thermostat, a season switch movable between two control positions, means for interconnecting sai'd thermostat with said source of power and said damper motor for controlling the furnac damper and whensaid season switch is in one control position, said means including a relay having an actuating winding and normally closed and normally opened contacts, conductors interconnecting said winding with said source of power to energize 'the same and'close said normally opened contacts to connect said motor to the source of season switch to the other control position deener'gi'zes said winding irrespective of the position of said room thermostat, and means interconnecting said thermostat with said source of power and said solenoid when said season switch is in the other control position.

CARL H. DICKE. 

